Good Steaming Conditions for Walnut

Getting lots of hot, wet steam is the trick — but it's not easy to achieve. October 1, 2010

QuestionAt our facility, we steam walnut at 205 degrees with 100% humidity. We keep it in there for 72 hours and then pull it. The sapwood is a little darker, but still too light for my liking. I received some walnut from another supplier, and their steaming job in most boards was awesome. The sapwood was pretty well as dark as the heartwood. I have tried to do this numerous times, but it is always a little lighter than the heartwood. Is anyone doing something differently? Longer time in the steamer? Does it have to be freshly sawn to get this final colour?

Forum Responses(Sawing and Drying Forum)
From contributor A:The hotter, the better, as well as the wetter the steam. Is your steam bubbling up through water? Are your packs getting to temp on the inside? 212 degrees is not too high a temp if you can get there. The lower the temp, the longer the time. The greener the lumber, the better the color of the steaming. I have a small chamber that I steam some in and when I saw the logs, it is dead stacked and in the chamber the same day for steaming. Hot as I can get it as fast as I can get it there. Wish I could get a pressure chamber.

From Professor Gene Wengert, forum technical advisor:I agree with contributor A. In fact, it is very difficult to get 205 F temperature and also 100% RH in most structures. The walls need to be 205 or hotter to avoid condensation and lowering the humidity; in most structures, this means a lot (not just 2") of insulation. Sometimes the walls, floor and roof are heated. Your 72 hours is long enough for 4/4. As contributor A says, the steam must be boiled through water to assure it is 100% RH. But this is not good enough if the walls are cool.

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